Tectonic Processes and Hazards
Enquiry Question 1 - Why are some locations more at risk from tectonic disasters?
Earthquakes
- 70% on the ‘Pacific Ring of Fire’
- Oceanic fracture zone
- Continental fracture zone
- Intraplate
Volcanic eruptions
- 75%+ on the ‘Pacific Ring of Fire’
- 5% on hotspots
Tsunamis
- 90% on the Pacific Basin
- Subduction zones off of the coast of Japan
1.1 The global distribution of 1. Convergent
tectonic hazards can be → Oceanic/ continental (subduction)
explained by plate boundary - Deep ocean trenches
and tectonic processes - Fold mountains
- Earthquakes at benioff zone
- Volcanoes with high silica content and andesitic
lava
→ Oceanic/ oceanic
- Deep ocean trenches
- Underwater volcanoes
- Island arcs
- Deep focus shallow earthquakes
→ Continental/ continental
- High fold mountains
- NO VOLCANOES
- Shallow focus earthquakes
2. Divergent
- Mid ocean ridges
- Rift valleys – plates move apart, crust stretches
and breaks into fault and land collapses
- Submarine volcanoes + effusive
- Form new islands on land
3. Conservative
- Causes powerful earthquakes – stick, pressure
+ stress, slip
- NO VOLCANOES
Intraplate earthquakes e.g Rhine rift valley/ African rift
valley
1. Ancient faults
2. Solid crust cracks over time due to collisions
3. Small magnitudes
Hotspot volcanoes + plumes e.g Hawaii
1. Unusual heat from magma causes magma
plume
2. Plume melts rock and crust
3. Weakens the crust
, 4. Magma shoots out
5. Magma cools to form igneous rock, sides of
volcano
6. Plate moves and process repeats
7. Chains of volcanoes
8. When volcanoes become inactive they form
islands or mountains
1. Mantle convection
1) Radioactive decay and residual heat from core
2) Hot rises towards asthenosphere
3) Hot rock hits solid lithosphere and forced
sideways
4) Far from core so cools
5) Sinks back to the outer core
6) Outer core made of dense material so forced
sideways again
7) Continues in a circular motion
8) Forces lithosphere to move by creating a weak
‘pull’ on plates above
2. Slab pull
1) Cracks between plates (usually oceanic)
2) Hot magma rises between gap
3) Newly formed crust at mid-ocean ridges
4) Cools and becomes heavier than hot mantle
beneath it
5) Density causes plate to sink into mantle
6) Plate moves
3. Seafloor spreading
1) Hot magma forced up from the asthenosphere
2) Hardens to form new oceanic crust
3) New crust pushes oceanic plates apart
4) Rift valley formed on land
→ Paleomagnetism (evidences new crust creation)
- Confirmed seafloor spreading
1. Every 400,000 years the earth’s magnetic field
changes direction
2. Lava cools and becomes rock
3. Minerals in rock line up with polarity at the time
4. Studying shows same pattern of magnetic field
on either side of ridge
4. Subduction
- If new crust is created then earth should be
expanding yet it isn’t so must be destroyed as
well
1) Oceanic plate moves towards continental
2) Oceanic plate subducts as it’s denser
1.2 There are theoretical - Subduction = destructive
frameworks that attempt to - Mantle convection = transform/ collision
explain plate movements - Slab pull = collision
- Seafloor spreading = constructive
→ Divergent (constructive) – North America + Eurasian
plates
, → Convergent (destructive) – South America + Nasca
plates
→ Conservative (San Andreas fault) – North American
+ Pacific plates
→ Collision (continental plates) – NEPAL –
Indo-Australian + Eurasian plates
1. Convergent
- Frequent collisions
- Volcanoes with andesitic lava
- Oceanic/ continental then earthquakes at benioff
zone
- Tend to be deep focus shallow earthquakes
2. Divergent
- Frequent underwater earthquakes
- Shallow earthquakes with low magnitude
- Effusive volcanoes and submarine
3. Conservative
- NO VOLCANOES
- Infrequent earthquakes
- More destructive earthquake as stress builds up
1. Earthquake waves (used to determine earth’s
interior)
1) P wave (primary)
- Highest frequency
- Moves through solid rock and fluid
- Compressional waves as it pushes and pulls
2) S wave (secondary)
- Slower than p waves
- Moves through solid rock – outer core
- Move side to side perpendicular to wave travel
3) L wave (love)
- Lowest frequency
- Fastest surface wave – responsible for damage
- Moves in a horizontal motion so side to side
1. Earthquake secondary hazards
1) Liquefaction e.g 1964 Niigata
- Soil behaves like a liquid
- Buildings collapse, road damages, bridge
damages, telecom and gas damage
1. Granular soils are made of a mix of soil and
pore spaces
2. Soils are hard due to compressed particles
3. Earthquake shock causes water molecules to
move up from high pressure to low pressure
4. Solid particles sink down
1. 3 Physical processes 5. Overall volume of soil and grains decreases
explain the causes of tectonic 6. Watery matrix
hazards 2) Landslides e.g 1994 Northridge caused 11000
- Where slops weaken and fail
- Occurs at magnitude above 4 ]Travel long
distances and grow in size
Exacerbating factors:
, 1. Magnitude
2. Summer monsoon rainfall
3. Landscape disturbances e.g trees
3) Tsunamis e.g Tohoku 2011
- Destructive and large spatial area extent
1. Volcanic eruption primary hazards
1) Volcanic gases e.g Kilauea
- Dissolved gases in magma
- Water vapour: lahars
- Sulphur dioxide: blocks sun and cause acid rain
- Fluorine gas: contaminates water/ farmland and
poisonous
2) Tephra and ashfall e.g Mount St Helens
- Bury crops and vegetation
- Breathing difficulties
- Roof collapses
- Start fires on ground
3) Lava flows e.g Kilauea
- Very hot 1170 degrees
- Moves very slow
- Destroy everything in path
4) Pyroclastic flows 2.g 1902 Mont Pelee
- Mixture: hot rock, lava and ash
- Material: glass shards, crystals, pumice and ash
- 1000 degrees
- Move faster
- Thick deposits leads to river flooding
- Can burn or poison
2. Volcanic eruption secondary hazards
1) Lahars e.g 1991 Mount Pinatubo
- Eruption melts snow or ice
- Volcanic mudflows of fine sand and silt
- Rainfall can trigger old tephra deposits and
surge downstream
Exacerbating factors
1. Slope gradient
2. Volume of material
3. Particle sizes
2) Jokulhaups e.g 2010 Eyjafjallajokull
- Glacial outburst flood
- Heat of eruption melts ice and snow in glacier
- Landform modification by erosion, washes
everything away, catch people unaware
1. Tsunamis e.g Tohoku 2011
→ Water column displacement and friction of sea bed
- Caused by releases in energy: Earthquakes,
landslides, volcanic eruptions
- They are low in height so go unnoticed
- Friction at base of wave slows down, shortens
wavelength and waves build in height
Exacerbating factors
1. Duration
Enquiry Question 1 - Why are some locations more at risk from tectonic disasters?
Earthquakes
- 70% on the ‘Pacific Ring of Fire’
- Oceanic fracture zone
- Continental fracture zone
- Intraplate
Volcanic eruptions
- 75%+ on the ‘Pacific Ring of Fire’
- 5% on hotspots
Tsunamis
- 90% on the Pacific Basin
- Subduction zones off of the coast of Japan
1.1 The global distribution of 1. Convergent
tectonic hazards can be → Oceanic/ continental (subduction)
explained by plate boundary - Deep ocean trenches
and tectonic processes - Fold mountains
- Earthquakes at benioff zone
- Volcanoes with high silica content and andesitic
lava
→ Oceanic/ oceanic
- Deep ocean trenches
- Underwater volcanoes
- Island arcs
- Deep focus shallow earthquakes
→ Continental/ continental
- High fold mountains
- NO VOLCANOES
- Shallow focus earthquakes
2. Divergent
- Mid ocean ridges
- Rift valleys – plates move apart, crust stretches
and breaks into fault and land collapses
- Submarine volcanoes + effusive
- Form new islands on land
3. Conservative
- Causes powerful earthquakes – stick, pressure
+ stress, slip
- NO VOLCANOES
Intraplate earthquakes e.g Rhine rift valley/ African rift
valley
1. Ancient faults
2. Solid crust cracks over time due to collisions
3. Small magnitudes
Hotspot volcanoes + plumes e.g Hawaii
1. Unusual heat from magma causes magma
plume
2. Plume melts rock and crust
3. Weakens the crust
, 4. Magma shoots out
5. Magma cools to form igneous rock, sides of
volcano
6. Plate moves and process repeats
7. Chains of volcanoes
8. When volcanoes become inactive they form
islands or mountains
1. Mantle convection
1) Radioactive decay and residual heat from core
2) Hot rises towards asthenosphere
3) Hot rock hits solid lithosphere and forced
sideways
4) Far from core so cools
5) Sinks back to the outer core
6) Outer core made of dense material so forced
sideways again
7) Continues in a circular motion
8) Forces lithosphere to move by creating a weak
‘pull’ on plates above
2. Slab pull
1) Cracks between plates (usually oceanic)
2) Hot magma rises between gap
3) Newly formed crust at mid-ocean ridges
4) Cools and becomes heavier than hot mantle
beneath it
5) Density causes plate to sink into mantle
6) Plate moves
3. Seafloor spreading
1) Hot magma forced up from the asthenosphere
2) Hardens to form new oceanic crust
3) New crust pushes oceanic plates apart
4) Rift valley formed on land
→ Paleomagnetism (evidences new crust creation)
- Confirmed seafloor spreading
1. Every 400,000 years the earth’s magnetic field
changes direction
2. Lava cools and becomes rock
3. Minerals in rock line up with polarity at the time
4. Studying shows same pattern of magnetic field
on either side of ridge
4. Subduction
- If new crust is created then earth should be
expanding yet it isn’t so must be destroyed as
well
1) Oceanic plate moves towards continental
2) Oceanic plate subducts as it’s denser
1.2 There are theoretical - Subduction = destructive
frameworks that attempt to - Mantle convection = transform/ collision
explain plate movements - Slab pull = collision
- Seafloor spreading = constructive
→ Divergent (constructive) – North America + Eurasian
plates
, → Convergent (destructive) – South America + Nasca
plates
→ Conservative (San Andreas fault) – North American
+ Pacific plates
→ Collision (continental plates) – NEPAL –
Indo-Australian + Eurasian plates
1. Convergent
- Frequent collisions
- Volcanoes with andesitic lava
- Oceanic/ continental then earthquakes at benioff
zone
- Tend to be deep focus shallow earthquakes
2. Divergent
- Frequent underwater earthquakes
- Shallow earthquakes with low magnitude
- Effusive volcanoes and submarine
3. Conservative
- NO VOLCANOES
- Infrequent earthquakes
- More destructive earthquake as stress builds up
1. Earthquake waves (used to determine earth’s
interior)
1) P wave (primary)
- Highest frequency
- Moves through solid rock and fluid
- Compressional waves as it pushes and pulls
2) S wave (secondary)
- Slower than p waves
- Moves through solid rock – outer core
- Move side to side perpendicular to wave travel
3) L wave (love)
- Lowest frequency
- Fastest surface wave – responsible for damage
- Moves in a horizontal motion so side to side
1. Earthquake secondary hazards
1) Liquefaction e.g 1964 Niigata
- Soil behaves like a liquid
- Buildings collapse, road damages, bridge
damages, telecom and gas damage
1. Granular soils are made of a mix of soil and
pore spaces
2. Soils are hard due to compressed particles
3. Earthquake shock causes water molecules to
move up from high pressure to low pressure
4. Solid particles sink down
1. 3 Physical processes 5. Overall volume of soil and grains decreases
explain the causes of tectonic 6. Watery matrix
hazards 2) Landslides e.g 1994 Northridge caused 11000
- Where slops weaken and fail
- Occurs at magnitude above 4 ]Travel long
distances and grow in size
Exacerbating factors:
, 1. Magnitude
2. Summer monsoon rainfall
3. Landscape disturbances e.g trees
3) Tsunamis e.g Tohoku 2011
- Destructive and large spatial area extent
1. Volcanic eruption primary hazards
1) Volcanic gases e.g Kilauea
- Dissolved gases in magma
- Water vapour: lahars
- Sulphur dioxide: blocks sun and cause acid rain
- Fluorine gas: contaminates water/ farmland and
poisonous
2) Tephra and ashfall e.g Mount St Helens
- Bury crops and vegetation
- Breathing difficulties
- Roof collapses
- Start fires on ground
3) Lava flows e.g Kilauea
- Very hot 1170 degrees
- Moves very slow
- Destroy everything in path
4) Pyroclastic flows 2.g 1902 Mont Pelee
- Mixture: hot rock, lava and ash
- Material: glass shards, crystals, pumice and ash
- 1000 degrees
- Move faster
- Thick deposits leads to river flooding
- Can burn or poison
2. Volcanic eruption secondary hazards
1) Lahars e.g 1991 Mount Pinatubo
- Eruption melts snow or ice
- Volcanic mudflows of fine sand and silt
- Rainfall can trigger old tephra deposits and
surge downstream
Exacerbating factors
1. Slope gradient
2. Volume of material
3. Particle sizes
2) Jokulhaups e.g 2010 Eyjafjallajokull
- Glacial outburst flood
- Heat of eruption melts ice and snow in glacier
- Landform modification by erosion, washes
everything away, catch people unaware
1. Tsunamis e.g Tohoku 2011
→ Water column displacement and friction of sea bed
- Caused by releases in energy: Earthquakes,
landslides, volcanic eruptions
- They are low in height so go unnoticed
- Friction at base of wave slows down, shortens
wavelength and waves build in height
Exacerbating factors
1. Duration
